With the advance of digital technology in recent years, apparatus handling AV (audio/visual) data is increasing. Handling of such AV data is also required in computers. AV data includes image data and audio data generally consisting of a large data amount. By employing data compression method such as the MPEG in order to reduce data amount, and employing a large capacity storage medium, it is possible to handle such AV digital data in writing and reading to/from a storage medium.
As such storage media, DVD (digital video disk), MO (magneto-optical disk), hard disk, semiconductor memory, and VTR tape (videotape) are currently in use. When reading AV data from such storage media, readout error may possibly occur in a read block during the readout of data blocks. This is caused by either degraded performance of the drive head or a defect of the storage medium. In addition, for example when the data are being downloaded, an error data may be stored without correction because audio/visual data is transferred continuously, which may also cause a read data error afterwards.
In respect of computer data, which includes program data and file data, a program is no more correctly executable in the event of a failure in such data. Therefore, on detection of a data error, retry processing is carried out without transferring of error data.
Meanwhile, in respect of AV data including image data and/or audio data, it is required to continue to record and read such data so as not to interrupt. In other words, it is not preferable to suspend data transfer even if a data error occurs.
As a measure against the aforementioned problem to be applied in computer storage apparatus, there has been proposed a method for continuing data transfer in the read processing of AV data, instead of interrupting, without detecting a data error (for example, in the official gazette of Japanese Unexamined Patent Publication No. Hei-11-144381). This method is based on that audio/visual data, produces no significant influence to the reproduced images even when errors occurred in a few blocks, because AV data is utilized as image reproduction etc.
There has also been disclosed for VTR reproduction apparatus having data compression capability, in which error correction is performed against AV data being read from a video tape (for example, in the official gazette of Japanese Unexamined Patent Publication No. Hei-5-274808, and Hei-7-272414). With regard to an error data block to which the error correction is not possible, the data is replaced by a pseudo data to output to data expansion (decompression) circuit, thereby degradation in the image quality is avoided.
In the above-mentioned methods, either a data having suffered an error or a pseudo data is transferred without modification so that continuous reproduction is possible for AV data requiring continuity of images or voices.
However, when such processing for reproducing AV data is executed by software (an application program) being employed in a system, it is not possible to apply such art straightly. Because such an application program processes the compressed data directly, it is not possible to reproduce when the application receives a data which was unexpected. This may produce to fail in normal application operation or the system may even be hung up.
In other words, error data may sometimes result in producing an unexpected data for the application, and thus producing a failure in normal application operation. Further, because the aforementioned pseudo data is constructed by a data to decrease image deterioration after being expanded by an expansion (decompression) circuit, it becomes difficult for the application to identify the error. This raises a problem that a more desirable reproduction processing such as skipping or interpolation is not applicable.
Furthermore, the aforementioned methods are the methods for error handling against a data failure when the data can be read out successfully from a storage medium. On the other hand, when a whole block data cannot be read out from a storage medium at all, the readout processing is interrupted. This impedes continuous readout of the audio/visual data. There are cases that dust or vibration, for example, on a magneto-optical disk may cause such a failure in reading out a block, producing the interruption against the continuous data readout.
Secondly, according to such conventional arts, reproduction processing is carried out straightly against such an error data or a pseudo data. Therefore, when the application writes the AV data including the error to read out the application possibly writes error AV data into another recording medium (for example, memory card), into such a storage medium.
To cope with this problem, it is to be considered to introduce a retry control against an error block so as not to process the error data, as having been applied in storage apparatus of a computer system mentioned earlier. For example, one known method is that, in a disk unit having an alternate sector to be substituted for an error sector, an error sector location is memorized while data blocks are continuously read out for one command. Each sector data (including error data) is transferred for the command, and thereafter the data in the alternate sector is read out to transfer to a host (for example, as disclosed in the official gazette of Japanese Unexamined Patent Publication No. Hei-1-300475).
According to this method, the data are continuously transferred, as is required for AV data. However, the data transferred to a host is a clean data in which an error has been excluded by means of a retry operation, because this operation is that the object data is a program data in this case. Accordingly, even when the reproduction is being carried out in the host (application), the retry is performed regularly and thus clean data is transferred in any case. However, once the reproduction is performed, the clean data being received after the reproduction becomes of no use. Instead, this merely results in an increased load in the application of the host.
Accordingly, it is an object of the present invention to provide a method for read processing of a storage medium, enabling an application to identify an error and to perform an appropriate reproduction processing even when AV data are transferred continuously from a storage medium, and to provide its storage apparatus, data reproduction method, data reproduction system, and a storage medium.
It is another object of the present invention to provide a method for read processing of a storage medium to transfer AV data continuously even when the data cannot be read out from a storage medium at all, and to provide its storage apparatus, data reproduction method, data reproduction system, and a storage medium.
It is another object of the present invention to provide a method for read processing of a storage medium, enabling an application to obtain a clean data when necessary even when AV data including an error is transferred, and to provide its storage apparatus, data reproduction method, data reproduction system, and a storage medium.